Process and apparatus for loading a particulate solid into a vertical tube

ABSTRACT

A process is described in which an elastic fluid is contacted with a particulate solid. This comprises providing a substantially vertical elongate tubular containment zone ( 1 ) containing a charge of the particulate solid ( 5 ), the volume of the containment zone ( 1 ) being greater than the settled volume of the particulate solid ( 5 ). An upper retainer means ( 3 ) is mounted at the upper end of the containment zone ( 1 ), the upper retainer means ( 3 ) being permeable to the fluid but adapted to retain particulate solid ( 5 ) in the containment zone ( 1 ). A follower means ( 4 ) is movably mounted in the containment zone ( 1 ) beneath the charge of particulate solid ( 5 ) for movement upwardly from the lower end of the containment zone ( 1 ) upon upward flow of elastic fluid through the containment zone ( 1 ) at a rate beyond a threshold rate. In the process the elastic fluid is caused to flow upwardly through the containment zone ( 1 ) at a rate which is sufficient to cause particulate solid ( 5 ) to rise up towards the upper end of the containment zone and form a cushion of particulate solid ( 5 ) against the underside of the upper retainer means ( 3 ). This rate is in excess of the threshold rate so as to cause the follower means ( 4 ) to move upwardly until it abuts against the underside of the cushion of particulate solid ( 5 ). The invention also provides an apparatus suitable for carrying out such a process and a method of loading a particulate solid into a substantially vertical tube.

1. TECHNICAL FIELD OF THE INVENTION

[0001] This invention relates to a process for contacting an elasticfluid with a particulate solid.

2. BACKGROUND OF THE INVENTION

[0002] There are many processes which involve contact between an elasticfluid, such as a gas or vapour, and a particulate solid. Thus manychemical processes are carried out using gas phase or vapour phasereaction conditions in which a gas or vapour stream is contacted with aparticulate catalyst. Other processes in which an elastic fluid iscontacted with a particulate solid include drying, in which a gas orvapour is contacted with a desiccant, and adsorption, in which a gas orvapour is contacted with an absorbent for the purpose of, for example,adsorption of potential catalyst poisons therefrom.

[0003] In such processes the particulate catalyst or other particulatesolid is frequently in the form of a fixed bed, although some processesare operated using a fluidised catalyst bed.

[0004] The conditions used in such processes often include highoperating temperatures and/or high pressures. Hence reactors may have towithstand high thermal and pressure stresses. Typical constructionalmaterials for chemical process vessels accordingly include mild steel,high pressure steel, stainless steel and other special steels andalloys.

[0005] The use of catalysts, supported catalysts and other particulates,such as desiccants and adsorbents, in fixed bed applications is thuswidespread. The particulate matter forming the fixed bed is typicallyceramic in nature or formed from pelletised metal oxides. Usually it hasa lower coefficient of expansion than the reactor, tube or othercontainment device for the particulate solid which is often composed ofmetal for pressure strength reasons. Thus, when the system increases intemperature, the particulate material slumps in the reactor because,upon heating, the walls of the reactor expand more than do the catalystparticles. Then when the temperature is later lowered, the walls of thereactor contract as it cools and the particulate matter may be caught asif by a tightening corset and thereby subjected to a crushing force,particularly if the particulate solid is contained in a substantiallyvertical metal tube.

[0006] In many applications the temperature variations in operation arenot very high and the different amounts of expansion between theparticulate matter and the containment device are not significant.Consequently excessive attrition of the particulate material or damageto container walls is not caused. However, in so-called fired processeswhich utilise high temperature operations, typically involvingcombustion in order to maintain the temperature in endothermic catalyticprocesses such as steam reforming, or in exothermic catalytic processessuch as partial oxidation processes, the amounts of expansion involvedare considerable. If the fixed bed is contained in a large diameterreactor or containment device, this differential expansion can beaccommodated with only minor attrition of the catalyst particles sincethere are many particles and cumulative small movements of the catalystparticles into internal voidage will occur. However, if the catalystparticles are contained in a narrow vertical tube having, for example, anominal diameter of less than about 6 inches (about 15.24 cm), thisrelative movement is insufficient and very high crushing forces can begenerated. This tends to result in attrition of the particulate matter,if friable to any degree, or in damage to the tube wall, if not. Thelatter phenomenon has been observed with physically strong aluminacatalyst support balls in high temperature reformer tubes. Furthermore,in cases where the vertical tubes are very long and experienceconsiderable expansion over their length due to the high operatingtemperature being used, for example steam reformer tubes, theparticulate matter drops by a very significant amount but cannot riseback up the tube when it cools due to being tightly squeezed by thecooling tube, a factor that exacerbates the crushing tendency.

[0007] Repeated heating and cooling cycles lead to a deterioration inthe desired characteristics of the packed bed, in that the originallyloaded volume of particulates is compressed to a higher density, therebyincreasing the pressure drop. In addition it has been found thatincreased pressure drop through a catalyst bed can be caused by, amongstother reasons, breakage of catalyst particles resulting from incorrectcharging of the catalyst or from differential expansion and contractionbetween the catalyst and the containing vessel due to temperaturecycling at start-up and shut-down. The breakage of catalyst particlesgives fragments of a smaller particle diameter, while erosion of thecorners of particles gives a lower voidage due to the eroded particlespacking more closely together. For further discussion reference may bemade to “Catalyst Handbook”, 2nd Edition, by Martyn V. Twigg (WolfePublishing Ltd., 1989), at page 125. This increased pressure dropgenerally increases the costs associated with gas compression in allfixed bed applications. In parallel fixed bed applications this can leadto increasing maldistribution, especially in a multi-tubular reactor,thereby causing different conversions and selectivities in differenttubes. This, in turn, can lead to further problems such as carbonlaydown, formation of hot spots (leading to possible tube failure and/orto sintering of the catalyst), and to development of different rates ofcatalyst deactivation which can further exacerbate the situation. Lossof catalyst surface material by spalling and attrition is particularlyserious when the active part of the catalyst is in the form of a shallowsurface layer, because in this case considerable catalyst activity canbe lost or the catalyst activity can become maldistributed.

[0008] The debris from the crushing forces will accumulate in the, bynow, more dense bed and also increase the pressure drop. There will bean increased likelihood of different pressure drops between differenttubes in a multi-tubular reactor leading to maldistribution of the gasor vapour. In addition, the position of the top of the bed within anyindividual tube will be difficult to predict.

[0009] Another problem occurs with externally fired tubular reactors,such as reformers, in that any part of the tube that does not containcatalyst is liable to overheat, with a consequent danger of tubefailure, since there is no endothermic reaction being catalysed in thatpart of the tube to absorb the radiant heat and hence to cool that partof the tube. This makes it important to determine as closely as possiblethe position of the catalyst bed during operation so as to minimise therisk of tube failure through local overheating.

[0010] There is, therefore, a need in the art to provide a reactordesign which overcomes the problems associated with crushing ofparticulate materials when the reactor is subjected to temperaturecycles of heating to high temperatures followed by cooling again, andwhich allows low pressure drop through the particulate material,minimises pressure drop build-up, and allows the position of the bed tobe fixed with a high degree of certainty so as to minimise the risk oftube failure in an externally fired reactor.

[0011] This need has been recognised previously and there are variousexamples in the prior art of attempts to overcome the problems outlinedabove.

[0012] The crushing of catalysts by radial forces due to widetemperature cycles in tubular reactors, such as steam reformingreactors, has been recognised in U.S. Pat. No. 4,203,950 (Sederquist).In this document it is proposed that the catalyst should be arranged inan annulus with at least one wall being flexible.

[0013] In U.S. Pat. No. 5,718,881 (Sederquist et al.) a steam reformerhas segmented reaction zones with individual supports for differenttemperature zones, the volume of the segments of catalyst beinginversely proportional to the temperature of the various zones in thereformer.

[0014] The use of flexible louvered screens to accommodate particlemovement is proposed in U.S. Pat. No. 3,818,667 (Wagner). Louvers arealso proposed in a catalytic converter for catalytically treating theexhaust gases from an internal combustion engine in U.S. Pat. No.4,063,900 (Mita et al.), and in U.S. Pat. No. 4,052,166 (Mita et al.).

[0015] It is proposed in U.S. Pat. No. 3,838,977 (Warren) to use springsor bellows in a catalytic muffler to control bed expansion andcontraction so as to maintain a compacted non-fluidised or lifted bed.Spring loading to maintain a bed of carbon granules tightly packedwithin a fuel vapour storage canister housing is described in U.S. Pat.No. 5,098,453 (Turner et al.).

[0016] A ratchet device to follow the decrease in volume of a bed butrestrain back-movement of an upper perforated retaining plate isproposed in U.S. Pat. No. 3,628,314 (McCarthy et al.). Similar devicesare described in U.S. Pat. No. 4,489,549 (Kasabian), in U.S. Pat. No.4,505,105 (Ness), and in U.S. Pat. No. 4,554,784 (Weigand et al.).

[0017] Pneumatic sleeves inside a catalyst bed to restrain movement ofthe particulate material are proposed in U.S. Pat. No. 5,118,331(Garrett et al.), in U.S. Pat. No. 4,997,465 (Stanford), in U.S. Pat.No. 4,029,486 (Frantz), and in U.S. Pat. No. 4,336,042 (Frantz et al.).

[0018] However, these prior art proposals are elaborate and do not solvesatisfactorily the problem of crushing of particulate catalysts whichcan be caused by repeated temperature cycling of a reactor tube.

[0019] Catalysts are usually passed over a screen to remove dust andbroken pieces either before shipment and/or before loading into areactor. Such removal of dust and broken pieces of catalyst is desirablein order to minimise the pressure drop across the reactor caused by thecatalyst bed. This screening step constitutes a costly procedure both interms of finance and time. Once loaded, catalyst particles usuallycannot be re-arranged and the packed density only tends to increase.

[0020] The loading of catalysts can be achieved by a number of methodsto reduce breakage and damage caused by free fall loading. For example,“sock” loading can be used in which the catalyst is put into long“socks”, usually made of fabric, which are folded or closed at one endwith a releasable closure or tie which can be pulled to release catalystwhen the sock is in position. Another method, which is more suitable foruse in forming beds in vessels of large diameter, for example from about0.75 m to about 4 m or more in diameter, than for loading tubes ofdiameter less than about 25 cm, is so-called “dense” loading in whichthe catalyst is fed through a spinning distributor so as to lay downconsecutive level layers rather than mounds of dumped catalyst. A thirdmethod, which is suitable for loading vertical tubes, utilises wiredevices or wires in tubes which reduce falling velocities. One option isto utilise one or more spirals of wire inside the tube so that thecatalyst particles bounce their way down the tube and do not undergofree fall over the full height of the tube. As the tube is filled, sothe wire or wires is or are withdrawn upwardly, optionally with verticalfluctuations. Such devices are proposed, for example, in U.S. Pat. No.4,077,530 (Fukusen et al.).

[0021] A further possibility is to use a line having spaced along itslength a series of brush-like members or other damper members and towithdraw the line upwardly as the catalyst particles are fed into thetube, as described in U.S. Pat. No. 5,247,970 (Ryntveit et al.).

[0022] “Sock” loading can also be carried out semi-continuously in largediameter vessels with a funnel and a filled fabric or solid tube whichis moved and raised to release the catalyst with frequent levelling ofthe catalyst.

[0023] Each method of loading produces fixed beds with different bulkdensities. The density differences can be quite marked; for example,with cylindrical particulate materials or extrudates the “dense” loadeddensity can be as much as about 18% greater than the corresponding“sock” loaded density due to the particles being laid generallyhorizontally and parallel to each other in the “dense” method ratherthan at random following “sock” removal.

[0024] In some applications it is desirable to maximise the amount ofcatalyst loaded, despite increased pressure drop through the fixed bed,in which case “dense” loading or loading into liquid may be used and/orthe tubes may be vibrated.

[0025] U.S. Pat. No. 5,892,108 (Shiotani et al.) proposes a method forpacking a catalyst for use in gas phase catalytic oxidation ofpropylene, iso-butylene, t-butyl alcohol or methyl t-butyl ether withmolecular oxygen to synthesise an unsaturated aldehyde and anunsaturated carboxylic acid in which metal Raschig rings are used asauxiliary packing material.

[0026] In U.S. Pat. No. 5,877,331 (Mummey et al.) there is described theuse of a purge gas to remove fines from a catalytic reactor for theproduction of maleic anhydride which contains catalyst bodies. In thisprocedure the purging gas, such as air, is passed through the catalystbed at a linear flow velocity sufficient to fluidise the catalyst finesbut insufficient to fluidise the catalyst bodies. At column 15 lines 16to 18 it is said:

[0027] “In order to prevent fluidization or expansion of the catalystbed during further operation of the reactors, and in particular toprevent the catalyst bodies in the fixed catalyst bed from abradingagainst one another or against the tube walls, a restraining bedcomprising discrete bodies of a material substantially denser than thecatalyst was placed on top of the column of catalyst in each tube of thereactors.”

[0028] It is also taught that this upflow removes undesirable fineparticles which, if left in the densely packed vessel, may contribute toplugging of the bed.

[0029] In U.S. Pat. No. 4,051,019 (Johnson) there is taught a method forloading finely divided particulate matter into a vessel for the purposeof increasing the packing density by introducing a fluid mediumcounter-current to the downward flow of the finely divided particulatematter at a velocity selected to maximise the apparent bulk density ofthe particulate matter in the vessel. It is taught that this method alsoprovides a method of removing undesirable fine particles which, if leftin the densely packed vessel, might contribute to plugging of the bed.

[0030] Vibrating tubes with air or electrically driven vibrators and/orstriking with leather-faced hammers is described in the afore-mentionedreference book by Twigg at page 569, the latter being used to furthercompact the catalyst in those tubes showing low pressure drop inmulti-tube applications, in order to achieve equal pressure drops ineach tube.

[0031] An upflow tubular steam reformer is described in U.S. Pat. No.3,990,858 (O'Sullivan et al.). In this proposal fluidisation of theparticulate material in the catalyst tubes is prevented by providing aweighted conically shaped hollow member which rests on top of the bed ofparticulate material. This conically shaped hollow member is providedwith elongated slots whereby fluid exiting from the bed flows into theinterior of the hollow member, through the slots and into the tubeoutlet.

[0032] There is a need to obviate in a simple and reliable way theproblems caused by crushing or attrition of particulate materials, suchas catalysts, desiccants or adsorbents, which are subjected to cyclingbetween high and low temperatures in vessels, particularly vessels madeof relatively high thermal expansion materials, such as steel or othermetals or alloys. There is also a need to provide a method of operatinga catalytic reactor in which the pressure drop across a catalyst bed canbe reliably minimised in operation. In addition there exists a need fora method of loading a tubular reactor with a particulate material, e.g.a particulate catalyst, in which the presence of “fines” can besubstantially avoided in the catalyst tube. Furthermore there exists aneed for a method of operating a reactor containing a charge of aparticulate material in which any “fines” which may be formed during thecourse of extended operation of the reactor can be removed simply fromthe reactor without having to discharge the charge of particulate solidfrom the reactor. There is also a need for operating a tubular reactorin which the position of the top of the bed of catalyst or otherparticulate material in the or each tube is known with certainty.

3, SUMMARY OF THE INVENTION

[0033] The present invention accordingly seeks to provide a novelprocess for effecting contact between an elastic fluid, such as a gas orvapour, and a particulate solid under conditions which include use ofcycling between elevated temperatures and ambient or near ambienttemperature but under which crushing of the solid particles isminimised. It further seeks to provide an improved process in which agas or vapour is contacted with a particulate solid, such as a catalyst,desiccant or adsorbent, which is subjected to elevated temperatures ofseveral hundreds of degrees Centigrade and then cooled withoutsubjecting the particulate solid to undue mechanical stresses. Inaddition, the present invention seeks to provide a process forcontacting a gas or vapour with a particulate solid in a tube atelevated temperatures under conditions which minimise imposition ofcrushing forces on the solid, particularly during cooling of the tube,and which facilitate removal of fragments of the particulate solidformed by attrition of the particles of catalyst or other solid so assubstantially to obviate any significant increase of pressure drop.Furthermore the invention seeks to provide a new and improved method ofpacking a catalyst bed. Yet another objective of the present inventionis to provide a method of operating a catalytic reactor tube packed withcatalyst particles wherein the position of the top of the catalyst bedis known with certainty despite the use of elevated temperatures whichcause the reactor tube to expand both longitudinally and radially. Theinvention further seeks to provide a method of operating a catalyticreactor, more particularly a tubular reactor in which a gaseous orvaporous phase is contacted with a particulate catalyst, so that thepressure drop across the catalyst bed is minimised. It also seeks toprovide a method of loading a tubular reactor with a particulatematerial, such as a particulate catalyst, in which the production ofundersized “fines” particles is substantially obviated and in which anysuch “fines” particles can be removed from the catalyst bed withoutfirst discharging the catalyst from the reactor.

[0034] According to one aspect of the present invention there isprovided a process in which an elastic fluid is contacted with aparticulate solid, which process comprises the steps of:

[0035] (a) providing a substantially vertical elongate tubularcontainment zone containing a charge of the particulate solid, thevolume of the containment zone being greater than the settled volume ofthe charge of particulate solid;

[0036] (b) providing upper retainer means mounted at the upper end ofthe containment zone, the upper retainer means being permeable to thefluid but adapted to retain particulate solid in the containment zone,and follower means movably mounted in the containment zone beneath thecharge of particulate solid for movement upwardly from the lower end ofthe containment zone upon upward flow of elastic fluid through thecontainment zone at a rate beyond a threshold rate; and

[0037] (c) causing the elastic fluid to flow upwardly through thecontainment zone at a rate which is sufficient to cause particulatesolid to rise up towards the upper end of the containment zone and forma cushion of particulate solid against the underside of the upperretainer means and which is in excess of the threshold rate so as tocause the follower means to move upwardly until it abuts against theunderside of the cushion of particulate solid.

[0038] The invention further provides an apparatus for effecting contactof an elastic fluid with a particulate solid comprising:

[0039] (a) reactor means defining a substantially vertical elongatetubular containment zone for containing a charge of the particulatesolid, the volume of the containment zone being greater than the settledvolume of the charge of the particulate solid;

[0040] (b) upper retainer means mounted at the upper end of thecontainment zone, the upper retainer means being permeable to the fluidbut adapted to retain particulate solid in the containment zone; and

[0041] (c) follower means movably mounted in the containment zonebeneath the charge of particulate solid for movement upwardly from thelower end of the containment zone upon upward flow of elastic fluidthrough the containment zone at a rate beyond a threshold rate;

[0042] whereby upon causing the elastic fluid to flow upwardly throughthe containment zone at a rate which is sufficient to cause particulatesolid to rise up towards the upper end of the containment zone and forma cushion of particulate solid against the underside of the upperretainer means and which is in excess of the threshold rate the followermeans moves upwardly until it abuts against the underside of the cushionof particulate solid.

[0043] The elastic fluid may comprise a gaseous or vaporous medium.

[0044] The upper retainer means is permeable to the elastic fluid butadapted to retain undamaged particles of the particular solid in thecontainment zone. It may comprise a screen of substantially parallelbars, rods or wires, or a wire mesh or other perforate form of retainer,such as a plate formed with numerous apertures.

[0045] The follower means is desirably designed so that there is a gapor gaps through and/or around it for upward flow of elastic fluidtherethrough. Moreover the lower end of the containment zone isdesirably designed so that, when there is no upward flow of elasticfluid through the containment zone, yet there is a gap or gaps forelastic fluid to flow upwardly through or around the follower means whensuch upward flow commences but remains below the threshold rate. Thusthe follower means typically includes a piston portion which is a loosefit in the containment zone so that fluid can pass up through an annulargap surrounding the piston portion. This piston portion can be disposedat or towards the lower end of the follower means, at or towards theupper end of the follower means, or intermediate the upper and lowerends of the follower means. One of the functions of the follower meansis to support the charge of particulate solid when any upward flow offluid is insufficient to cause particulate solid to rise upwardly in thecontainment zone to form a cushion against the underside of the upperretainer means. If the piston portion is at or near the upper end of thefollower means, then the piston portion can perform this function; ifnot, then the follower means preferably includes, at or towards itsupper end, support means for supporting the charge of particulate solidwhen any upward flow of fluid is insufficient to cause particulate solidto rise upwardly in the containment zone to form a cushion ofparticulate solid against the underside of the upper retainer means, forexample a series of concentric rings spaced one from another so that thegaps between adjacent pairs of rings are insufficient to allow aparticle of predetermined size of the particulate solid to passtherethrough. Such gaps also assist in distributing the flow ofupflowing elastic fluid more uniformly across the cross-section of thecontainment zone.

[0046] Instead of using concentric rings it is alternatively possible touse a mesh arrangement to provide support for the charge of particulatesolid when any upward flow of elastic fluid is insufficient to causeparticulate solid to rise upwardly in the containment zone to form acushion of particulate solid against the underside of the upper retainermeans.

[0047] The follower means should further be designed so that, despitethe annular gap around the piston portion, the follower means cannottilt sufficiently from a vertical position to become jammed against thewalls of the containment zone. In one design this is achieved byproviding the piston portion with a series of substantially verticalplates radiating from a vertical axis, for example three vertical platesin a Y-section arrangement, the plates being arranged vertically withtheir planes at angles of approximately 120° to one another around asubstantially vertical axis of course more than three plates can beused, if desired, for example four plates arranged vertically in anx-section at 90

to one another around a substantially vertical axis.

[0048] Alternatively, the piston portion can be provided with a centralvertical rod with one or more spider sets formed by three or more rodsor bars radiating from the central vertical rod, for example threeradiating rods set at an angle of approximately 120° to one another andpositioned so as to prevent the follower means from tilting asignificant amount as it moves within the containment zone and hencefrom jamming against the walls of the containment zone. In this way thefollower means can allow elastic fluid to pass freely at all timesaround it in either the upward or downward direction, while ensuringthat, as the rate of upward flow of elastic fluid is increased to a ratebeyond the threshold rate, the follower means lifts smoothly off fromits position at the bottom end of the containment zone and then moves upthe containment zone until it abuts against the underside of the cushionof particulate solid.

[0049] When the elastic fluid flows upwardly at a low flow rate throughthe containment zone, the follower means remains at the lower end of thecontainment zone with the particulate solid supported on it in the formof a bed. As the upward flow rate increases, the particles of theparticulate solid become fluidised at the upper end of the bed. Uponstill further increase of the upward flow rate, the proportion of thebed that is fluidised increases until particles begin to rise up thecontainment zone and form a cushion of particles against the undersideof the upper retainer means. When the upward flow rate is sufficient forsubstantially all of the particles to have lifted, some of the particleson the lower side of the cushion of particles tend to fall off and thenbe carried up again. At an upward flow rate beyond the threshold flowrate, the follower means is lifted and comes to abut against theunderside of the cushion of particles thereby holding the cushion ofparticles in place and preventing particles from falling off the cushionof particles while the follower means remains in place against theunderside of the cushion of particles.

[0050] The elongate containment zone may be one of a plurality ofelongate containment zones connected in parallel, for example it may bea catalyst tube mounted in the furnace of a steam reformer.

[0051] Preferably at least part of the containment zone is ofsubstantially uniform horizontal cross-section. More preferably thecontainment zone is of substantially uniform horizontal cross-sectionthroughout at least a major part of its height and even more preferablythroughout substantially all of its height.

[0052] The follower means is adapted to rise upwardly up the containmentzone when the upward flow rate of elastic fluid is greater than thethreshold flow rate until it abuts against the cushion of particulatesolid. Thus at least that part of the containment zone in which thefollower means moves should desirably be of uniform horizontal crosssection. For example it may comprise a tube of substantially circularcross section.

[0053] In a preferred embodiment the containment zone comprises a tubewhich has a length:diameter ratio of from about 50:1 to about 1000:1,more preferably from about 100:1 to about 750:1. Normally such a tubehas an internal diameter of about 6 inches (about 15.2 cm) or less,preferably an internal diameter of about 2 inches (about 5.08 cm) orless, e.g. a tube having an internal diameter of from about 1 inch(about 2.54 cm) to about 2 inches (about 5.08 cm).

[0054] In many cases it is possible to design the containment zone sothat the distance through which the follower means rises up thecontainment zone in operation is at most only a few inches, for examplefrom about 1 inch (about 2.54 cm) up to about 10 inches (about 25.40cm), preferably from about 2 inches (about 5.08 cm) to about 5 inches(about 12.70 cm), e.g. about 3 inches (about 7.62 cm).

[0055] Although it will frequently be preferred for the containment zoneto be of substantially uniform cross-section throughout its height, itis alternatively possible for a lower portion of the containment zone inwhich the follower means moves in operation to have a smaller area ofcross-section than an upper part of the containment zone. Hence thecontainment zone can comprise a lower tubular portion of relativelysmall diameter attached to the bottom of a tube of larger diameter. Inthis case, while the narrower lower portion of the containment zone inwhich the follower means moves in operation requires to be machined to arelatively close tolerance, the transverse dimensions of the upperportion of the containment zone do not have to be so carefullycontrolled. A further advantage in such an arrangement is that the gapbetween the follower means and the walls of the lower portion of thecontainment zone can be larger than if the follower means is arranged toslide in a larger tube. Again this factor reduces the need for carefulmachining of the inside of that part of the containment zone in whichthe follower means moves.

[0056] It will usually be preferred that the follower means is arrangedto block passage of elastic fluid up or down the containment zone butpermit upward passage of elastic fluid through a clearance gap betweenthe internal surface of the containment zone and the follower means, theclearance gap providing a clearance less than the smallest dimension ofa non-fragmented particle of the particulate solid. Hence the followermeans may comprise a closed lower end portion for defining the clearancegap and an upper portion provided with elastic fluid passing means. Suchelastic fluid passing means may comprise a plurality of substantiallyconcentric rings spaced one from another, the clearance between adjacentrings being less than the smallest dimension of a non-fragmentedparticle of the particulate solid. Alternatively the elastic fluidpassing means may comprise a perforate baffle member whose perforationsare smaller the smallest dimension of a non-fragmented particle of theparticulate solid.

[0057] The containment zone may contain a plurality of types ofparticulate solid, in which case each type can be separated from anadjacent type by means of a respective follower means.

[0058] Typically the particulate solid has at least one dimension lessthan about 10 mm, e.g. about 6 mm. The particulate solid may besubstantially spherical in shape and have, for example, a diameter offrom about 2 mm to about 10 mm, e.g. about 6 mm. However, other shapesof particulate solid can alternatively be used but the use of shapeswhich can easily form bridges should be avoided. Thus other shapes whichcan be used include rings, saddles, pellets, cylindrical extrudates,trilobates, quadrilobates, or the like.

[0059] Examples of suitable particulate solids include catalysts,desiccants and adsorbents.

[0060] One method of loading the particulate solid into the containmentzone involves loading via the top of the containment zone against agentle upflow stream of elastic fluid at a rate less than that requiredto lift fully any already charged particulate solid (or to move thefollower means upwardly) but such that the particulate solid does notfall freely under gravity. In this way the danger of damage to theparticulate solid can be significantly reduced or substantiallyeliminated.

[0061] Any other method of loading, e.g. “sock” loading, can, however,be used. Other techniques that can be used include the use of wiredevices, the use of devices as described in U.S. Pat. No. 5,247,970(Ryntveit et al.), or the like.

[0062] After initial loading of the particulate solid and optionallymounting in position the upper retainer means, the pressure drop acrossthe containment zone can be measured in upflow or downflow mode,whereupon, after applying an upflow stream of elastic fluid to theparticulate solid with the upper retainer means in position, the settledvolume of particulate solid in the containment zone and/or the pressuredrop across the containment zone can be checked, particulate solid beingadded to, or removed from, the containment zone if the settled volume ofparticulate solid in the containment zone does not correspond to apredetermined value and/or if the pressure drop across the containmentzone is not within the desired range. Hence in a preferred procedure,after initial loading of the particulate solid, the pressure drop acrossthe containment zone is measured in a measurement step. Then particulatesolid can be added to or removed from the containment zone if thepressure drop measured does not conform to a predetermined value.Alternatively, or in addition, after initial loading of the particulatesolid the settled volume of particulate solid in the containment zonecan be measured in a measurement step, whereafter particulate solid maybe added to or removed from the containment zone if the settled volumeof particulate solid in the containment zone does not conform to apredetermined value. In either case, after initial loading of theparticulate solid but prior to the measurement step, elastic fluid canbe caused to flow upwardly through the containment zone at a rate inexcess of the threshold rate so as to cause the particulate solid toform a cushion of particulate solid against the underside of the upperretainer and so as to cause the follower means to rise up thecontainment zone until it abuts against the underside of the cushion ofparticulate solid, thereafter the upward flow of elastic fluid beingreduced or discontinued so as to permit formation of a settled bed ofparticulate solid.

[0063] In one particularly preferred process according to the inventionthe particulate solid is a catalyst effective for catalysing a desiredchemical reaction, e.g. steam reforming, and an elastic fluid comprisinga reaction feed mixture capable of undergoing the desired chemicalreaction is passed in upflow mode through the containment zone while thecontainment zone is maintained under operating conditions effective forcarrying out the desired chemical reaction. In an alternative processaccording to the invention the particulate solid is a catalyst effectivefor catalysing a desired chemical reaction, and an elastic fluidcomprising a reaction feed mixture capable of undergoing the desiredchemical reaction is passed in downflow mode through the containmentzone while the containment zone is maintained under operating conditionseffective for carrying out the desired chemical reaction.

[0064] In the process of the invention the containment zone and theparticulate solid can be subjected to an elevated temperature, forexample a temperature of at least about 500° C. For example, the desiredchemical reaction may be a partial oxidation reaction, in which case theelastic fluid comprises a partial oxidation feed mixture, theparticulate solid is a partial oxidation catalyst, and the temperatureof the containment zone and the partial oxidation catalyst is maintainedby the partial oxidation reaction. Alternatively the desired chemicalreaction may be a steam reforming reaction, in which case the elasticfluid comprises a steam reforming feed mixture, the particulate solid isa steam reforming catalyst, and the temperature of the containment zoneand the steam reforming catalyst is maintained by hot combustion gasesexternal to the containment zone.

[0065] The invention further provides a method of loading a particulatesolid into a substantially vertical tube in readiness for conducting amethod in which an elastic fluid is contacted with the particulatesolid, which method comprises the steps of:

[0066] (a) providing a substantially vertical elongate tubular reactorhaving an elongate containment zone for containing a charge of aparticulate solid;

[0067] (b) providing at the lower end of the containment zone followermeans movably mounted in the containment zone for movement upwardly fromthe lower end of the containment zone upon upward flow of elastic fluidthrough the containment zone at a rate beyond a threshold rate;

[0068] (c) loading a predetermined charge of the particulate solid intothe containment zone on top of the follower means, the settled volume ofthe particulate solid being less than the volume of the containmentzone;

[0069] (d) mounting at the upper end of the containment zone upperretainer means permeable to the fluid but adapted to retain particulatesolid in the containment zone; and

[0070] (e) causing an elastic fluid to flow upwardly through thecontainment zone at a rate which is sufficient to cause particulatesolid to rise up towards the upper end of the containment zone and forma cushion of particulate solid against the underside of the upperretainer means and which is in excess of the threshold rate so as tocause the follower means to move upwardly until it abuts against theunderside of the cushion of particulate solid. In such a method saidparticulate solid may be loaded via the top of said containment zoneagainst an upflow stream of elastic fluid at a rate less than thatrequired to lift fully said particulate solid but such that saidparticulate solid does not fall freely under gravity. Preferably, afterapplying an upflow stream of elastic fluid to said particulate solid,the settled volume of particulate solid in the containment zone ischecked. Particulate solid can be added to or removed from thecontainment zone if the settled volume of particulate solid in thecontainment zone does not conform to a predetermined value.

[0071] In a particularly preferred loading method the upward flow ofelastic fluid is maintained in step (e) for a period and at a ratesufficient to cause substantially all particles which are smaller than apredetermined design particle size and are sufficiently small to passthrough the upper retainer means to pass through the upper retainermeans.

4. BRIEF DESCRIPTION OF THE DRAWINGS

[0072]FIG. 1 is a semi-diagrammatic side view of a vertical reactor tubehaving a catalyst follower therein with no upward gas flow;

[0073]FIG. 2 is a side view of the vertical reactor tube of FIG. 1 withan upward gas flow at a rate in excess of a threshold gas flow rate;

[0074]FIG. 3 is a side view of the catalyst follower of FIGS. 1 and 2 onan enlarged scale;

[0075]FIG. 4 is a top plan view of the catalyst follower of FIG. 3;

[0076]FIG. 5 is a perspective view from above of an alternative catalystfollower; and

[0077]FIG. 6 is a perspective view from below of the catalyst followerof FIG. 5.

5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0078] Referring to FIG. 1 of the drawings, there is shown a verticalreactor tube 1 for carrying out a gas phase or vapour phase reaction,such as a steam reforming process. This process can be operated inupflow or downflow mode, as desired. However, for reasons which will befurther explained below, upflow mode is preferred in the practice of thepresent invention.

[0079] Tube 1 is circular in cross section and has an internal diameterof about 2 inches (about 5.08 cm) and is provided with an internalannular ledge 2, or with a removable support with a central verticalaperture, and with an upper perforate retainer 3. It can be made of anysuitable material that is substantially inert under the reactionconditions to be used. For, example, it can be a stainless steel oralloy tube or a mild steel tube, depending upon the nature of thereaction to be carried out and the reaction pressure.

[0080] Although reactor tube 1 for convenience usually has a circularcross section, tubes of other cross sections, such as elliptical,hexagonal, or square cross section may be used, if desired.

[0081] The length of reactor tube 1 is a multiple (which can be either awhole number multiple, e.g. 100×, or a fractional number multiple, e.g.37.954×) of the diameter or other transverse dimension of the reactortube 1. Although reactor tube 1 as illustrated is relatively short, itwill be appreciated by those skilled in the art that reactor tube 1 canbe of any convenient length. For example, reactor tube 1 can be about 6feet (about 182.88 cm) long or more, e.g. up to about 30 feet (about914.40 cm) or 45 feet (about 1371.60 cm) or more, if desired.

[0082] When there is no upward flow of gas or vapour, ledge 2 supports acatalyst follower 4 on top of which is disposed a charge 5 of aparticulate catalyst. The settled volume of the charge 5 of particulatecatalyst, whether this is densely packed or loosely packed, is less thanthe available volume between the top of the catalyst follower 4 and theupper perforate retainer 3.

[0083] The catalyst particles may be of any desired size or shape butare typically substantially spherical. Typically the catalyst particleshave no dimension which is smaller than about 3 mm. They may besubstantially spherical particles which have, for example, a diameter ofabout 6 mm. However, the particles may have any other desired shape, forexample, cylinders (optionally with one or more passages formedtherein), cylindrical extrudates, or trilobe or quadrilobe extrudates,so long as the shape of the particles is not conducive to the formationof bridges. The catalyst particles are sufficiently large not to passthrough any annular gap between catalyst follower 4 and the internalwall of reactor tube 1 nor to pass through upper perforate retainer 3.

[0084] The upper perforate retainer 3 is intended to prevent passage ofundamaged catalyst particles upwardly beyond upper perforate retainer 3.It will, however, allow dust or small fragments of abraded catalyst topass upwardly therethrough. It may consist of or include a wire gauze ormesh of appropriate mesh size.

[0085] Catalyst follower 4 is made from a suitable material, such asstainless steel, and comprises three plates 6 welded together axiallyand symmetrically so as to form a Y-section central portion with theplates 6 set at 120° to one another about a vertical axis. The radiallyouter edges of plates 6 are closely spaced from the internal wall ofreactor tube 1 and help to maintain catalyst follower 4 in an uprightposition and guide it in its movement up and down the reactor tube 1 asfurther described below.

[0086] As can be seen from FIGS. 1 and 2, and more clearly from FIG. 3,the upper part 7 of each plate has a stepped profile and annular rings8, 9, 10, and 11 are welded to this stepped profile. The clearancebetween the annular rings 8, 9, 10, and 11 is less than the averagesmallest dimension of the catalyst particles and the lateral dimensionsof the rings are so chosen that the catalyst particles cannot drop downthrough catalyst follower 4 but are retained on the upper side thereof.Near the lower end of catalyst follower 4 the plates 6 are welded to adisc 12 below which there are also welded lower plates 13.

[0087] There is an annular gap 14 around disc 12 to allow upward passageof gas or vapour. In addition there is a central aperture 15 at the topend of catalyst follower 4, as can be seen in FIG. 4. However, when gasor vapour passes up reactor tube 1 at a flow rate in excess of athreshold flow rate, disc 12 acts as a loose piston and so catalystfollower 4 rises in reactor tube 1. The weight of the catalyst follower4 is so selected, and the size and shape of the catalyst follower 4 areso chosen, that the upward lifting forces due to the upflowing gas orvapour at such a flow rate cause catalyst follower 4 to float up thetube 1 thereby sweeping any non-fluidised particulate material before itand compressing the cushion of particles 5 against the fixed upperperforate retainer 3.

[0088] It will be seen that catalyst follower 4 includes a lower spacersection constituted by plates 13 which serves to hold the piston partformed by disc 12 away from the ledge 2 mounted in tube 1 when there isno upflow of elastic fluid and when catalyst follower 4 is supported onledge 2. This results in gas or vapour being able, at all times, to passfreely in upflow or in downflow past this piston part. Disc 12 allowssmooth lift of the catalyst follower 4 in upflow operation. The weightof catalyst follower 4 is selected so that, at the desired operatingupflow gas rate, the uplift force caused by the pressure loss across theannular gap 14 between the disc 12 and the inside wall of reactor tube 1is greater than the gravitational pull of the total mass of the catalystfollower 4.

[0089]FIG. 2 illustrates the reactor tube 1 when gas or vapour isflowing up the reactor tube 1 at a flow rate in excess of a thresholdflow rate. The catalyst particles have lifted to form a cushion ofcatalyst particles 5 abutting against the underside of upper perforateretainer 3. In addition catalyst follower 4 has also lifted and isitself pressing against the underside of the cushion of catalystparticles 5.

[0090] By varying the size of the portions cut out of the radially outersides of plates 6, it is possible to alter the weight of the catalystfollower 4. It accordingly becomes possible to vary the threshold flowrate, i.e. the upward flow rate of gas or vapour within a given tube 1at which the catalyst follower 4 will lift from ledge 2.

[0091] If desired, concentric rings 8, 9, 10, and 11 can be replaced bya gauze or lattice arrangement.

[0092] An alternative form of catalyst follower 24 is illustrated inFIGS. 5 and 6. This is cast from a suitable alloy. This comprises abottom disc 25 below which are three spacer elements 26 that are set at120° to one another and that serve to support catalyst follower 24 onthe ledge 2 when there is no upflow of gas through reactor tube 1. Thegaps between spacer elements 26 and the annular gap around bottom disc25 serve to permit gas to flow upwards around catalyst follower 24 atlow gas velocities and to permit catalysts follower 24 to lift off fromledge 2 when the upward gas flow rate exceeds the threshold rate. Abovedisc 25 is a rod portion 27 from whose upper end project three steppedflanges 28, which are radially spaced one from another around the axisof the rod portion 27 by an angle of 120°. Secured to flanges 28 are aseries of rings 29, 30, 31 and 32, the spacing between adjacent ringsbeing less than the smallest dimension of an undamaged catalystparticle. In this way catalyst particles cannot pass down the tube belowcatalyst follower 24 whereas gas or other elastic fluid can pass up thetube at flow rates both below and above the threshold value at whichcatalyst follower 24 will lift off the ledge 2.

[0093] Instead of providing reactor tube 1 with an internal ledge 2, itis expedient to replace the ledge 2 by a number of small inwardlydirected projections, for example, 3 or 4 small projections, the spacesbetween which provide a passage for upward flow of elastic fluid pastbottom disc 25. In this case plates 13 or spacer elements 26 would notbe required. Alternatively ledge 2 can be replaced by a removablesupport device, which is formed with a central vertical aperture, so asto enable the reactor tube 1 to be emptied downwardly, if necessary.

[0094] The operation of a preferred process using the apparatus of FIGS.1 to 4 will now be described. The apparatus of FIGS. 5 and 6 can be usedin a similar way.

[0095] In order to load catalyst particles into tube 1 any suitablemethod can be used. For example, if the catalyst is sufficiently robust,upper perforate retainer 3 can be removed and the catalyst thencarefully poured in until the desired amount has been introduced. Sincereactor tube 1 is of relatively small cross section, the catalystparticles tend to collide with the walls of the tube and thus do notever undergo absolutely free fall. Hence their passage down the reactortube 1 results in their rattling their way down the tube 1 rather thanundergoing free fall. If the catalyst is of a frangible nature, then anyof the previously mentioned techniques using wires, wire coils, or thedevices of U.S. Pat. No. 5,247,970 (Ryntveit et al.) can be used.Alternatively the “sock” technique can be used, for example.

[0096] After loading of the catalyst charge the settled volume of thecatalyst can be measured and compared with a design value. If thatsettled volume is greater than or less than the design value, then someof the catalyst can be removed or more catalyst can be loaded, asappropriate. In addition, before the desired process, e.g. steamreforming or partial oxidation, is brought on line, it will usually bedesirable to install the upper perforate retainer 3 and to pass a gas,such as nitrogen, up the tube 1 at a rate in excess of the thresholdrate so as to cause the catalyst and the catalyst follower 4 to rise upthe tube 1 and form a cushion of catalyst particles immediately underthe upper perforate retainer 3. This upflow can be maintained for asufficient length of time and at a rate to allow substantially all“fines” particles with a particle size small enough to pass through theupper perforate retainer 3 to pass therethrough and be swept away by thegas. This procedure can be repeated as many times as necessary byreducing the gas flow until the catalyst follower 4 and catalyst fallback down the tube, and then increasing the flow of gas again past thethreshold rate. Then the pressure drop across the catalyst charge,either in upflow through the cushion of catalyst or in downflow throughthe settled bed of catalyst can be measured and compared to a designvalue. If either the settled volume or the pressure drop are not asdesired, then the upper perforate retainer 3 can be removed to permitmore catalyst to be added or some of the catalyst to be removed, asappropriate, and the procedure repeated until the measurements indicatethat the loading of catalyst in tube 1 is considered satisfactory.

[0097] If more than one type of catalyst is to be loaded into reactortube 1, then a further catalyst follower 4 can be added after each typeof catalyst has been loaded except after the final type of catalyst hasbeen loaded.

[0098] At low upflow rates the gas or vapour flows through the settledbed of catalyst particles. However, as the flow rate increases, so atleast some of the catalyst particles will tend to lift, forminginitially a partially fluidised bed above a lower static bed of catalystparticles. As the flow rate is increased, more and more of the catalystparticles are fluidised and travel up the reactor tube 1 to form acushion of catalyst particles against the underside of upper perforateretainer 3. Any dust or under-sized particles will tend to pass throughthe upper perforate retainer 3 during this procedure. Upon furtherincrease of flow rate, substantially all of the catalyst particles arelifted from on top of catalyst follower 4 into the cushion of catalystparticles with a relatively small number of particles in motion justunder the cushion of catalyst particles, these moving particles fallingaway from the cushion under gravity and then being carried back up againby the upflowing gas or vapour. Eventually, as the flow rate increasesstill further, the catalyst follower 4 moves upwards until it abutsagainst the underside of the cushion of catalyst particles, asillustrated in FIG. 2, thereby preventing any further movement of thecatalyst particles and thus possible attrition thereof.

[0099] During this procedure the upflowing elastic fluid may be an inertgas or a reactant gas required for pre-treatment of the catalyst. Forexample, in the case of a hydrogenation catalyst, the upflowing elasticfluid during this phase of operation may be a hydrogen-containing gasrequired for pre-reduction of the catalyst. Pre-treatment can beeffected at any appropriate temperature or pressure. Thus pre-treatmentcan be effected at ambient temperature or at elevated temperature, asappropriate, and can be effected at ambient pressure, at sub-ambientpressure, or at elevated pressure, as need be.

[0100] If reactor tube 1 is to be used in upflow mode, then followingany necessary pre-treatment of the catalyst particles in the cushion ofcatalyst particles, the flow of elastic fluid can be switched to thereactant gas or vapour mixture and any necessary adjustment of thetemperature or pressure carried out in order to allow an operatingcampaign to be carried out. For example, if the reactor tube 1 is a tubemounted in the furnace of a steam reformer, it may be heated to atemperature of 500° C. or more, for example to at least about 750° C. upto about 1050° C., and maintained under a pressure of, for example,about 100 psia to about 600 psia (about 698.48 kPa to about 4136.86kPa). In the course of being heated to the elevated operatingtemperature, the reactor tube 1 will expand radially and longitudinallyand the catalyst, having a lower expansion coefficient, will move tofill the increased space. However, the location of the top of thecushion of catalyst particles will be fixed at all times since theposition of the upper catalyst retainer 3 is known and remains fixed,while the bottom of the cushion will move upwards marginally. Thisfixing of the position of the top of the cushion of catalyst, i.e. thetop of the catalyst bed in operation, is of great advantage inmulti-tubular reactors, for example, where introduction of heat needs tobe precisely located relative to the catalyst, such as in the furnace ofa steam reformer, or where the level of a liquid coolant or heatingmedium outside the tubes needs to be located precisely relative to thecatalyst, such as in an exothermic reaction controlled by raising steamfrom a controlled level of boiling water, for example in Fischer-Tropschreactions, in hydrogenation reactions, or the like. In addition, it hasthe added benefit of substantially obviating the problem of tube failurethrough lack of control of the temperature within or outside a catalystfilled tube.

[0101] At the end of an operating campaign, the reactant feed can beswitched to an inert gas or to air, as appropriate, either before orafter allowing the pressure to return to standby or shutdown pressureconditions, while allowing the reactor tube 1 to cool. Alternatively, ifthe catalytic reaction is endothermic, the supply of heat to the outsideof the tubes can be reduced while maintaining a flow of precess fluidthrough the reactor tube 1 as it cools. Then the flow rate of elasticfluid can be reduced, thus allowing catalyst follower 4 and catalystparticles 5 to drop back in controlled fashion until catalyst follower 4again rests on ledge 2 (or on the removable support device, if ledge 2is replaced by a removable support device, as described above, so as toenable the reactor tube 1 to be cleared downwardly) and catalystparticles return gently to the condition illustrated in FIG. 1 withminimum damage to the catalyst.

[0102] On re-start in upflow mode, the catalyst will have been partiallyremixed. If reactor tube 1 is a tube of a multi-tubular reactor, thecatalyst particles will reform a consistent low packing density in allthe tubes, while fines and debris will be removed by the gas upflow.Hence the pressure drop across each tube will remain substantiallyconstant throughout the life of the catalyst.

[0103] During the cooling operation at the end of an operating campaignin upflow mode, the gas flow can be increased one or more times torecreate the cushion of catalyst particles against the underside ofupper perforate retainer 3, whereafter the gas flow can again be reducedin order to prevent the formation, during cooling of the reactor tube 1,of any “bridges” of catalyst particles, which could otherwise lead to adanger of crushing forces being exerted on the catalyst particles by thecontracting walls of the reactor tube 1 as it cools.

[0104] It is also possible to interrupt an upflow operating campaign byswitching the flow of elastic fluid to an inert gas, in the case of anexothermic catalytic reaction, or by reducing the rate of supply of heatto the outside of the reactor tube while maintaining a flow of processfluid through the reactor tube 1 in the case of an endothermic reaction,and then allowing the catalyst particles and catalyst follower 4 to dropby reducing the flow of inert gas or process fluid. The gas flow canthen be returned to a value which causes the cushion of catalystparticles to be re-formed. In the course of re-forming the cushion ofcatalyst particles, any dust or catalyst fragments will tend to passthrough the upper perforate retainer 3, thus removing a potential causeof undesired increase of pressure drop across the catalyst cushion.Thereafter the inert gas can be switched back to an upflowing reactantmixture, or the rate of heat supply can be increased, to continue theupflow operating campaign.

[0105] If reactor tube 1 is to be used in a downflow mode, then afterthe cushion of catalyst particles has been formed as shown in FIG. 2and, if desired any necessary pre-treatment of the catalyst has beeneffected, the upflow of gas or vapour is reduced and then graduallystopped thereby allowing the catalyst particles to settle out into acondition similar to that shown in FIG. 1. In this condition thecatalyst particles have a low packing density in the bed of catalystparticles. In downflow operation, as the reactor tube 1 reachesoperating temperature, especially if that operating temperature is over500° C. (for example, if reactor tube 1 is a tube in the furnace of asteam reformer), it will expand radially and longitudinally and thecatalyst, having a lower expansion coefficient, will tend to slump anddrop inside reactor tube 1. The location of the top of the catalyst bedat this point is not known with certainty. When the process is shutdown, the catalyst particles would normally be subjected to considerablecrushing forces. To obviate this danger, an upflow of suitableoptionally preheated gas can be initiated at a rate sufficient to liftthe catalyst particles within the tube 1 while the tube 1 and thecatalyst cool. This minimises crushing of the catalyst particles andre-orients the bed to a low packing density ready for re-start. Afurther advantage is that any fines and debris are removed at eachshut-down.

[0106] The reactor tube 1 may be, for example, a catalyst tube in thefurnace of a steam reformer. Since it is desirable to pack each catalysttube with catalyst in exactly the same manner so that the pressure dropacross each catalyst tube is substantially identical to thecorresponding pressure drop for every other catalyst tube of thereformer furnace, the catalyst tubes can be loaded in turn by thegeneral method described above. In this case an upflow of a gas, such asair, can be used in order to reduce the falling velocity of theparticulate catalyst material. This air flow can be applied solely tothe tube being loaded by plugging the upper ends of all other tubes andsupplying air to a common lower header space, or by applying air to thebottom of each tube in turn. The latter option is preferred becauseother operations can then be performed on the loaded tube while othertubes are being loaded.

[0107] The invention is further illustrated by means of the followingExamples.

EXAMPLE 1

[0108] A glass tube 1, which was 2 metres long with an internal diameterof 38.1 mm, was set up vertically with a follower 4 of the typeillustrated in FIGS. 1 to 4 initially positioned at its bottom end. Thisfollower 4 had a disc 12 of diameter 36 mm. A charge of 1.84 kg of anickel catalyst (nickel on calcia-alumina support catalyst balls ofnominal diameter 6 mm) was dropped carefully into the tube. Afterloading, the upper perforate retainer 3 was fitted at a desired heightin the tube 1. This retainer consisted of a Johnson wedge-wire screencomprising 1.5 mm wire with a 2 mm gap. The tube 1 was not filled fullyto allow for the lower bulk density of the catalyst during the tests.Compressed air was introduced via a pressure regulator and flowrotameter (not shown) to the bottom of the tube 1 at a rate at leastsufficient to lift the catalyst and the catalyst follower 4 such that aconsolidated cushion of catalyst balls 5 was formed at the top of thetube 1 immediately under the retainer 3. The height of the catalyst bed5 was measured before introducing air. The air flow was then reduced toallow the catalyst follower 4 to move back down to the bottom of tube 1and also to allow the catalyst balls to move back down to the bottom ofthe tube 1. This procedure was repeated a number of times, from whichdata the following average apparent bulk densities in kg/m³ weredetermined. The densities were found to be very repeatable, with thefollowing small variations over 360 tests during which the catalyst wasremoved and replaced after 10, 20 and 120 tests: After loading (freedrop) 1157 +/− 1.0% (over four loadings) Lifted (with air flow) 1017 +/−0.5% (within any one loading) Lifted (with air flow) 1017 +/− 1.5% (overall the tests) Dumped (with no air flow) 1000 +/− 0.5% (within any oneloading) Dumped (with no air flow) 1000 +/− 1.0% (over all the tests)

EXAMPLE 2

[0109] The weight of catalyst used in Example 1 was checked after 10,20, 120 and 360 tests and showed 0.38% weight loss over 360 tests. Inseparate tests in the same apparatus the flow resistance of the freshand worn catalyst particles used in Example 1 was compared. At an airflow rate of 49.14 Nm³/h the fresh catalyst particles exhibited apressure drop of 1.21×10⁵ Pa/m, while at an air flow rate of 48.96 Nm³/hthe worn catalyst particles, after 360 tests, exhibited a flowresistance of 1.22×10⁵ Pa/m.

EXAMPLE 3

[0110] The procedure of Example 1 was followed using 2.06 kg of nickelon α-alumina support catalyst balls of nominal diameter 6 mm from Dycat,Type 54/98. This catalyst support material is much more friable thanthat used in Examples 1 and 2 with only about 25% of the crush strengthof the catalyst used in Examples 1 and 2. The weight of the catalyst waschecked after 10, 60, 150, 300 and 390 tests and showed a total weightloss of 7.0% over 390 tests. During the tests catalyst fragmentsrepresented by this weight loss were visibly removed from the bed by thegas flow as dust. The amount lost in each group of tests decreased asfollows, expressed as average weight % lost per lift and drop cycle:0.085, 0.042, 0.026, 0.010, 0.009.

EXAMPLE 4

[0111] In separate tests in the same apparatus as was used in Examples 1to 3 the flow resistance of the fresh catalyst particles and of the worncatalyst particles, after 390 tests, was compared. At an air flow rateof 49.67 Nm³/h the fresh catalyst particles exhibited a pressure loss of1.15×10⁵ Pa/m, while at an air flow rate of 49.77 Nm³/h the worncatalyst particles exhibited a-pressure loss of 1.32×10⁵ Pa/m. Theincrease in pressure loss can be attributed to be due mainly to thereduced voidage (measured as 0.462 fresh and 0.449 worn) and the reducedsize of the worn particles (which was estimated to be equivalent to areduction in diameter, compared to the fresh catalyst particles, of 2%).This Example demonstrates that, because the process substantiallyremoves the fines resulting from particle wear, the process allows thepressure drop in operation to remain as low as can be practicallyexpected.

1. A process in which an elastic fluid is contacted with a particulatesolid, which process comprises the steps of: (a) providing asubstantially vertical elongate tubular containment zone containing acharge of the particulate solid, the volume of the containment zonebeing greater than the settled volume of the charge of the particulatesolid; (b) providing upper retainer means mounted at the upper end ofthe containment zone, the upper retainer means being permeable to thefluid but adapted to retain particulate solid in the containment zone,and follower means movably mounted in the containment zone beneath thecharge of particulate solid for movement upwardly from the lower end ofthe containment zone upon upward flow of elastic fluid through thecontainment zone at a rate beyond a threshold rate; and (c) causing theelastic fluid to flow upwardly through the containment zone at a ratewhich is sufficient to cause particulate solid to rise up towards theupper end of the containment zone and form a cushion of particulatesolid against the underside of the upper retainer means and which is inexcess of the threshold rate so as to cause the follower means to moveupwardly until it abuts against the underside of the cushion ofparticulate solid.
 2. A process according to claim 1, wherein theelongate containment zone is one of a plurality of elongate containmentzones connected in parallel.
 3. A process according to claim 1 or claim2, wherein at least part of said containment zone is of substantiallyuniform horizontal cross-section.
 4. A process according to claim 3,wherein at least part of said containment zone comprises a tube ofsubstantially circular cross section.
 5. A process according to claim 4,wherein at least part of said containment zone comprises a tube havingan internal diameter of about 6 inches (about 15.2 cm) or less.
 6. Aprocess according to claim 3 or claim 4, wherein at least part of saidcontainment zone comprises a tube having an internal diameter of about 2inches (about 5.08 cm) or less.
 7. A process according to any one ofclaims 1 to 6, wherein said follower means is arranged to block passageof elastic fluid up or down the containment zone apart from through aclearance gap between the internal surface of the containment zone andthe follower means, the clearance gap having a width less than thesmallest dimension of a non-fragmented particle of the particulatesolid.
 8. A process according to claim 7, wherein said follower meanscomprises a closed lower end portion for defining the gap means and anupper portion provided with elastic fluid passing means.
 9. A processaccording to any of claims 1 to 8, wherein said elastic fluid passingmeans comprises a plurality of substantially concentric rings spaced onefrom another, the clearance between adjacent rings being less than thesmallest dimension of a non-fragmented particle of the particulatesolid.
 10. A process according to any one of claims 1 to 9, wherein saidcontainment zone contains a plurality of types of particulate solid,each type being separated from an adjacent type by means of a respectivefollower means.
 11. A process according to any of claims 1 to 10,wherein said particulate solid has at least one dimension less thanabout 10 mm.
 12. A process according to any of claims 1 to 11, whereinsaid particulate solid is substantially spherical in shape.
 13. Aprocess according to any of claims 1 to 12, wherein said particulatesolid comprises a catalyst.
 14. A process according to any of claims 1to 13, wherein after initial loading of the particulate solid, thepressure drop across the containment zone is measured in a measurementstep.
 15. A process according to claim 14, wherein particulate solid isadded to or removed from the containment zone if the pressure dropmeasured does not conform to a predetermined value.
 16. A processaccording to any one of claims 1 to 13, wherein after initial loading ofthe particulate solid the settled volume of particulate solid in thecontainment zone is measured in a measurement step.
 17. A processaccording to claim 16, wherein particulate solid is added to or removedfrom the containment zone if the settled volume of particulate solid inthe containment zone does not conform to a predetermined value.
 18. Aprocess according to any one of claims 14 to 17, wherein after initialloading of the particulate solid but prior to the measurement stepelastic fluid is caused to flow upwardly through the containment zone ata rate in excess of the threshold rate so as to cause the particulatesolid to form a cushion of particulate solid against the underside ofthe upper retainer and so as to cause the follower means to rise up thecontainment zone until it abuts against the underside of the cushion ofparticulate solid, and thereafter the upward flow of elastic fluid isreduced or discontinued so as to permit formation of a settled bed ofparticulate solid.
 19. A process according to any of claims 1 to 18,wherein the particulate solid is a catalyst effective for catalysing adesired chemical reaction, and wherein an elastic fluid comprising areaction feed mixture capable of undergoing the desired chemicalreaction is passed in upflow mode through the containment zone while thecontainment zone is maintained under operating conditions effective forcarrying out the desired chemical reaction.
 20. A process according toany of claims 1 to 18, wherein the particulate solid is a catalysteffective for catalysing a desired chemical reaction, and wherein anelastic fluid comprising a reaction feed mixture capable of undergoingthe desired chemical reaction is passed in downflow mode through thecontainment zone while the containment zone is maintained underoperating conditions effective for carrying out the desired chemicalreaction.
 21. A process according to claim 19 or claim 20, wherein saidcontainment zone and said particulate solid are subjected to atemperature of at least about 500° C.
 22. A process according to claim21, wherein said desired chemical reaction is a partial oxidationreaction, wherein said elastic fluid comprises a partial oxidation feedmixture, wherein said particulate solid is a partial oxidation catalyst,and wherein the temperature of the containment zone and the partialoxidation catalyst is maintained by said partial oxidation reaction. 23.A process according to claim 21, wherein said desired chemical reactionis a steam reforming reaction, wherein said elastic fluid comprises asteam reforming feed mixture, wherein said particulate solid is a steamreforming catalyst, and wherein the temperature of the containment zoneand the steam reforming catalyst is maintained by hot combustion gasesexternal to said containment zone.
 24. Apparatus for effecting contactof an elastic fluid with a particulate solid comprising: (a) reactormeans defining a substantially vertical elongate tubular containmentzone for containing a charge of the particulate solid, the volume of thecontainment zone being greater than the settled volume of theparticulate solid; (b) upper retainer means mounted at the upper end ofthe containment zone, the upper retainer means being permeable to thefluid but adapted to retain particulate solid in the containment zone;and (c) follower means movably mounted in the containment zone beneaththe charge of particulate solid for movement upwardly from the lower endof the containment zone upon upward flow of elastic fluid through thecontainment zone at a rate beyond a threshold rate; whereby upon causingthe elastic fluid to flow upwardly through the containment zone at arate which is sufficient to cause particulate solid to rise up towardsthe upper end of the containment zone and form a cushion of particulatesolid against the underside of the upper retainer means and which is inexcess of the threshold rate the follower means moves upwardly until itabuts against the underside of the cushion of particulate solid. 25.Apparatus according to claim 24, wherein the elongate containment zoneis one of a plurality of elongate containment zones connected inparallel.
 26. Apparatus according to claim 24 or claim 25, wherein atleast part of said containment zone is of uniform horizontalcross-section.
 27. Apparatus according to claim 26, wherein at leastpart of said containment zone comprises a tube of substantially circularcross section.
 28. Apparatus according to claim 27, wherein at leastpart of said containment zone comprises a tube having an internaldiameter of about 6 inches (about 15.2 cm) or less.
 29. Apparatusaccording to claim 27 or claim 28, wherein at least part of saidcontainment zone comprises a tube having an internal diameter of about 2inches (about 5.08 cm) or less.
 30. Apparatus according to any one ofclaims 24 to 29, wherein said follower means is arranged to blockpassage of elastic fluid up or down the containment zone apart fromthrough a clearance gap between the internal surface of the containmentzone and the follower means, the clearance gap having a width less thanthe smallest dimension of a non-fragmented particle of the particulatesolid.
 31. Apparatus according to claim 30, wherein said follower meanscomprises a closed lower end portion for defining the gap means and anupper portion provided with elastic fluid passing means.
 32. Apparatusaccording to any of claims 24 to 31, wherein said elastic fluid passingmeans comprises a plurality of substantially concentric rings spaced onefrom another, the spacing between adjacent rings being less than thesmallest dimension of a non-fragmented particle of the particulatesolid.
 33. Apparatus according to any one of claims 24 to 32, whereinsaid containment zone is adapted for containing a plurality of types ofparticulate solid, each type being separated from an adjacent type bymeans of a respective follower means.
 34. Apparatus according to any ofclaims 24 to 33, wherein the particulate solid is a catalyst effectivefor catalysing a desired chemical reaction, further including means forpassing an elastic fluid comprising a reaction feed mixture capable ofundergoing the desired chemical reaction in upflow mode through thecontainment zone, and means for maintaining the containment zone underoperating conditions effective for carrying out the desired chemicalreaction.
 35. Apparatus according to any of claims 24 to 33, wherein theparticulate solid is a catalyst effective for catalysing a desiredchemical reaction, further including means for passing an elastic fluidcomprising a reaction feed mixture capable of undergoing the desiredchemical reaction in downflow mode through the containment zone, andmeans for maintaining the containment zone under operating conditionseffective for carrying out the desired chemical reaction.
 36. A methodof loading a particulate solid into a substantially vertical tube inreadiness for conducting a method in which an elastic fluid is contactedwith the particulate solid, which method comprises the steps of: (a)providing a substantially vertical elongate tubular reactor having anelongate containment zone for containing a charge of a particulatesolid; (b) providing at the lower end of the containment zone followermeans movably mounted in the containment zone for movement upwardly fromthe lower end of the containment zone upon upward flow of elastic fluidthrough the containment zone at a rate beyond a threshold rate; (c)loading a predetermined charge of the particulate solid into thecontainment zone on top of the follower means, the settled volume of theparticulate solid being less than the volume of the containment zone;(d) mounting at the upper end of the containment zone upper retainermeans permeable to the fluid but adapted to retain particulate solid inthe containment zone; and (e) causing an elastic fluid to flow upwardlythrough the containment zone at a rate which is sufficient to causeparticulate solid to rise up towards the upper end of the containmentzone and form a cushion of particulate solid against the underside ofthe upper retainer means and which is in excess of the threshold rate soas to cause the follower means to move upwardly until it abuts againstthe underside of the cushion of particulate solid.
 37. A methodaccording to claim 36, wherein the elongate containment zone is one of aplurality of elongate containment zones connected in parallel.
 38. Amethod according to claim 36 or claim 37, wherein said containment zoneis of uniform horizontal cross-section.
 39. A method according to claim38, wherein at least part of said containment zone comprises a tube ofsubstantially circular cross section.
 40. A method according to claim39, wherein at least part of said containment zone comprises a tubehaving an internal diameter of about 6 inches (about 15.2 cm) or less.41. A method according to claim 39 or claim 40, wherein at least part ofsaid containment zone comprises a tube having an internal diameter ofabout 2 inches (about 5.08 cm) or less.
 42. A method according to anyone of claims 36 to 41, wherein said follower means is arranged to blockpassage of elastic fluid up or down the containment zone apart fromthrough gap means between the internal surface of the containment zoneand the follower means, the gap means having a width less than thesmallest dimension of a non-fragmented particle of the particulatesolid.
 43. A method according to claim 42, wherein said follower meanscomprises a closed lower end portion for defining the gap means and anupper portion provided with elastic fluid passing means.
 44. A methodaccording to any of claims 36 to 43, wherein said elastic fluid passingmeans comprises a plurality of substantially concentric rings spaced onefrom another, the clearance between adjacent rings being less than thesmallest dimension of a non-fragmented particle of the particulatesolid.
 45. A method according to any of claims 36 to 44, wherein saidparticulate solid has at least one dimension less than about 10 mm. 46.A method according to any of claims 36 to 45, wherein said particulatesolid is substantially spherical in shape.
 47. A method according to anyof claims 36 to 46, wherein said particulate solid comprises a catalyst.48. A method according to any of claims 36 to 47, wherein the settledvolume of particulate solid in the containment zone is measured in ameasurement step.
 49. A method according to claim 48, whereinparticulate solid is added to or removed from the containment zone ifthe settled volume of particulate solid in the containment zone does notconform to a predetermined value.
 50. A method according to any ofclaims 36 to 49, wherein the method includes the following steps: (f)measuring the pressure drop across the containment zone in a measurementstep; and (g) comparing the measured pressure drop with a design value.51. A method according to claim 50, wherein particulate solid is addedto or removed from the containment zone if the measured pressure dropdoes not conform to the design value, whereafter the pressure drop ismeasured again.
 52. A method according to any one of claims 49 to 51,wherein after initial loading of the particulate solid but prior to themeasurement step elastic fluid is caused to flow upwardly through thecontainment zone at a rate in excess of the threshold rate so as tocause the particulate solid to form a cushion of particulate solidagainst the underside of the upper retainer means and so as to cause thefollower means to move upwardly until it abuts against the underside ofthe cushion of particulate solid, and thereafter the upward flow ofelastic fluid is discontinued so as to permit formation of a settled bedof particulate solid.
 53. A method according to any one of claims 36 to52, wherein said particulate solid is selected from a partial oxidationcatalyst and a steam reforming catalyst.
 54. A method according to anyone of claims 36 to 53, wherein in step (e) the upward flow of elasticfluid is maintained for a period and at a rate sufficient to causesubstantially all particles which are smaller than a predetermineddesign particle size and are sufficiently small to pass through theupper retainer means to pass through the upper retainer means.